The present invention relates to a method of making a hardened sheet metal part from a blank.
Nothing in the following discussion of the state of the art is to be construed as an admission of prior art.
International Publication NO. WO 99/07492 describes a method of making a hardened sheet steel product. A sheet steel blank is hereby hot stamped and rapidly cooled in a pair of cooled tools in a process called press hardening. The blank has holes that are collared by mandrels in connection with the forming. The collaring is carried out in unhardened material, but the collars harden directly when formed. The holes can be used for fasteners or they can be used as reference holes or receptacles for orientation of the sheet metal product. The need to pre-manufacture the holes in the blank is disadvantageous because the dimensional accuracy of the produced sheet metal product depends on the initial perforation. Circular holes may thus easily assume an oval shape during forming. When deviating from predefined tolerances, the produced sheet metal product becomes therefore useless. In particular when sheet metal products are involved that have complex geometries, the rate of rejects or waste increases substantially.
Although the execution of hot forming and hardening steps in a single press tool is efficient, any following cutting operation of the hardened sheet metal part is complex and cost-intensive, accompanied by substantial tool wear.
It would be desirable and advantageous to provide an improved method of making hardened sheet metal parts to obviate prior art shortcomings and to enable precise cutting operations on the sheet metal part.